Control device for controlling automatic engine stop and start

Cross-reference to related application

This application is related to and claims priority from Japanese Patent Applications No. 2010-3512 filed on Jan. 11, 2010 and No. 2010-265000 filed on Nov. 29, 2010, the contents of which are hereby incorporated by reference.

Background of the invention

1. Field of the invention

The present invention relates to control devices for controlling automatic engine stop and start. The control device is capable of automatically stopping the internal combustion engine of a vehicle on receiving an automatic engine stop request and automatically restarting the internal combustion engine on receiving an engine restart request.

2. Description of the related art

There is a recent trend for vehicles to be equipped with an automatic engine control system capable of automatically stopping and starting the internal combustion engine of a vehicle in order to improve fuel consumption and reduce exhaust gas emission. Such an automatic engine control system is called to as the "engine idle stop control system". The engine idle stop control system can automatically stop the engine when the driver intends to stop the vehicle, and automatically restart the engine when the driver of the vehicle operates various units in order to restart the engine, for example, the driver of the vehicle depresses the clutch pedal, releases the brake pedal, and operates a shift lever.

In general, the engine starter mounted to the internal combustion engine of a vehicle is comprised of an electric motor for pushing and rotating the pinion gear in order to engage with a ring gear fixed to the crank shaft of the internal combustion engine. This makes it possible for the pinion gear to be cranked with the ring gear fixed to the rotary shaft of the internal combustion engine of the vehicle. However, there is a possibility of generating large gear meshing noises and impacts due to the engagement when the pinion gear is meshed with the ring gear which is fixed to the crank shaft under a large difference of rotation speed between the pinion gear and the ring gear because the pinion gear cannot be smoothly meshed with the ring gear due to a large difference in rotation speed between them.

Conventional patent documents, for example, Japanese patent laid open publication No. JP 2002-122059 has disclosed a conventional technique which restarts the internal combustion engine of a vehicle by the following steps (a1) and (a2) when an engine restart request occurs when the rotation speed of the internal combustion engine is dropping immediately after the automatic engine stop of the internal combustion engine caused by the generation of an automatic engine stop request: (a1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine when the rotation speed of the internal combustion engine (or the rotation speed of the ring gear) almost zero, namely, when the engine almost stops; and (a2) After the step (a1), the starter motor rotates the pinion gear in order to start the cranking.

However, if the engine restart request occurs when the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, the above conventional technique disclosed in JP 2002-122059 increases a delay period of time counted from the time when an engine restart request occurs to the time when the internal combustion engine is actually restarted because the cranking must be performed by the starter motor in order to restart the internal combustion engine after the rotation speed of the internal combustion engine is almost zero, namely, the engine is almost stopped. This delay period of time may cause discomfort driving to the driver of the vehicle.

In order to solve the above conventional drawback, there are other conventional techniques disclosed in Japanese patent laid open publications No. JP 2005-330813 and JP 2002-70699, which restart the internal combustion engine of a vehicle by the following steps (b1) and (b2) when the engine restart request occurs when the period of the rotation speed of the internal combustion engine is dropping due to the occurrence of the automatic engine stop request and the stop of combustion of the internal combustion engine: (b1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine after the rotation speed of the pinion gear is synchronized with the rotation speed of the ring gear so as to decrease a difference in rotation speed between the pinion gear and the ring gear; and (b2) After the step (b1), the starter motor starts to rotate the pinion gear in order to perform the cranking.

However, the conventional techniques disclosed in JP 2005-330813 and JP 2002-70699 only show the engagement between the pinion gear and the ring gear when they are synchronized with each other, but do not disclose and suggest any technique to detect and determine an optimum time in order to smoothly and correctly mesh the pinion gear with the ring gear. That is, the conventional techniques do not disclose and suggest any technique to detect and determine the optimum time when the pinion gear is meshed with the ring gear.

Summary of the invention

It is an object of the present invention to provide a control device for controlling automatic engine stop and start capable of smoothly restarting the internal combustion engine of a vehicle even if an engine restart request occurs when the rotation speed of the internal combustion engine is dropping due to the occurrence of the automatic engine stop request and the stop of fuel combustion in the internal combustion engine.

To achieve the above purposes, the present invention provides a control device as a first aspect of the present invention. The control device performs automatic engine stop and start. The control device of the first aspect of the present invention has a starter, a first engine restart control means, a second engine restart control means, an engine restart ready control means, and a third engine restart control means.

The starter is comprised of a starter motor. The starter motor rotates a pinion gear and an actuator capable of meshing the pinion gear with a ring gear which is fixed to the crank shaft of an internal combustion engine. The starter independently drives the starter motor and the actuator, respectively. The control device is capable of stopping the internal combustion engine when an automatic engine stop request occurs, and restarting the internal combustion engine when an engine restart request occurs. The first engine restart control means executes a first engine restart control which restarts a fuel injection in order to restart the internal combustion engine without performing a cranking by the starter when the engine restart request occurs when the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when a current rotation speed of the internal combustion engine is within a first rotation speed range which is higher than a first rotation speed. The second engine restart control means executes a second engine restart control which drives the starter motor in order to synchronize the rotation speed of the pinion gear with the rotation speed of the ring gear, and drives the actuator to mesh the pinion gear with the ring gear in order to perform the cranking and restart the internal combustion engine when the rotation speed of the internal combustion engine is decreased by the automatic engine stop, and the engine restart request occurs when the current rotation speed of the internal combustion engine is within a second rotation speed range which is not more than the first rotation speed and higher than a second rotation speed. The engine restart ready control means executes an engine restart ready control of not driving the starter to perform the cranking when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the current rotation speed of the internal combustion engine is within a rotation speed ready range. The rotation speed ready range is not more than the second rotation speed and higher than a third rotation speed. After this control operation, the engine restart ready control means drives the actuator to mesh the pinion gear with the ring gear when the current rotation speed of the internal combustion engine is within a third rotation speed range which is not more than the third rotation speed, and after or during the above meshing operation, the engine restart ready control means drives the starter to perform the cranking by the starter motor. Further, the third engine restart control means executes a third engine restart control of driving the actuator to mesh the pinion gear with the ring gear when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the current rotation speed of the internal combustion engine is within the third rotation speed range which is not more than the third rotation speed, and after or during the above gear meshing operation, the engine restart ready control means drives the starter to perform the cranking by the starter motor in order to restart the internal combustion engine.

When the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the rotation speed of the internal combustion engine is within the first rotation speed range which is a high rotation speed range, the first engine restart control means in the control device having the above configuration determines that it is not necessary for the starter to perform any cranking. In this case, the control device restarts the fuel injection without performing any cranking in order to restart the internal combustion engine. This makes it possible for the control device to immediately restart the combustion in order to restart the internal combustion engine immediately when the engine restart request occurs. Further, because the control device does not drive the starter to perform the cranking, it is possible for the starter to have zero power consumption, and because the control device does not drives the starter motor to mesh the pinion gear with the ring gear under a large difference in rotation speed between the pinion gear and the ring gear, it is possible to avoid gear meshing noises from being generated.

Further, when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the rotation speed of the internal combustion engine is within the second rotation speed range, the second engine restart control means in the control device having the above configuration determines that it is impossible to smoothly mesh the pinion gear with the ring gear unless the rotation speed of the pinion gear is synchronized with the rotation speed of the ring gear because the rotation speed of the ring gear is higher than the rotation speed of the pinion gear. The second engine restart control means thereby executes the second engine restart control which drives the starter motor in order to synchronize the rotation speed of the pinion gear with the rotation speed of the ring gear and to decrease the difference in rotation speed between them. After this control, the second engine start control means drives the actuator to mesh the pinion gear with the ring gear in order to perform the cranking. Accordingly, it is possible to smoothly mesh the pinion gear with the ring gear and thereby restart the internal combustion engine while preventing gear meshing noises from being generated and decreasing a delayed period counted from the time of the generation of the engine restart request to the time when the internal combustion engine is restarted.

Still further, when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the rotation speed of the internal combustion engine is within the third rotation speed range which is a low rotation speed range, the third engine restart control means in the control device having the above configuration determines that it is possible to smoothly mesh the pinion gear with the ring gear without performing the synchronization in rotation speed between the pinion gear and the ring gear because the current rotation speed of the ring gear is lower than the rotation speed of the pinion gear. The third engine restart control means drives the actuator to mesh the pinion gear with the ring gear when the engine restart request occurs, and after or during this gear meshing operation, the third engine restart control means drives the starter to perform the cranking in order to restart the internal combustion engine.

This makes it possible to eliminate the synchronizing operation in rotation speed between the pinion gear and the ring gear while preventing gear meshing noises from being generated, and thereby possible for the starter to immediately start the cranking, and obtain the rapid engine restart and decrease the power consumption of the starter.

If the second rotation speed range and the third rotation speed range are continued without having the rotation speed ready range between the second and third rotation speed ranges, the following problem would be caused because the rotation speed of the internal combustion engine is oscillated and gradually decreased while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop.

FIG. 9 is a timing chart showing the above problem caused by the engine restart control. As shown in FIG. 9, because the rotation speed of the internal combustion engine is oscillated and gradually decreased while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, when the second rotation speed range and the third rotation speed range are adjacent with each other, the rotation speed is gradually decreased while the rotation speed oscillates around the boundary of the second rotation speed range and the third rotation speed range. Therefore when the engine restart request occurs even if the current rotation speed is within the second rotation range when the current rotation speed of the internal combustion engine is around the boundary between the second rotation speed range and the third rotation speed range, there is a possibility for the current rotation speed to immediately enter the third rotation speed range. On the other hand, when the engine restart request occurs even if the current rotation speed is in the third rotation range when the current rotation speed of the internal combustion engine is around the boundary between the second rotation speed range and the third rotation speed range, there is a possibility for the current rotation speed to immediately enter the second rotation speed range. This phenomenon requires a complicated control for estimating the rotation speed of the internal combustion engine with high accuracy, and the control device cannot execute the smooth engine restart control.

In order to solve the above problem, the control device according to the present invention has the engine restart ready control means which uses the rotation speed ready range between the second rotation speed range and the third rotation speed range.

When the engine restart request occurs in the rotation speed ready range, the engine restart ready control means does not drive the starter to perform the cranking. After this, when the rotation speed of the internal combustion engine is within the rotation speed ready range, the engine restart ready control means drives the starter motor to rotate the pinion gear in order to perform the cranking after driving the actuator to mesh the pinion gear with the ring gear or during the gear meshing operation. This makes it possible for the control device to smoothly restart the internal combustion engine without performing any complicated engine restart control for estimating the current rotation speed with high accuracy even if the engine restart request occurs during the rotation speed ready range at the boundary of the second rotation speed range and the third rotation speed range. In this control process by the engine restart ready control means, even if the engine restart request occurs when the rotation speed of the internal combustion engine is within the rotation speed ready range, the starter restarts the cranking and the internal combustion engine is thereby restarted after the rotation speed of the internal combustion engine is within the third rotation speed range. Because the period of time in which the rotation speed of the internal combustion engine passes through the rotation speed ready range is short, it is possible to set the delay period of time to an allowable delay period of time, where the delay period of time is a time period counted from the time when the engine restart request occurs to the time when the internal combustion engine is restarted.

In accordance with a second aspect of the present invention, there is provided a control device which is comprised of the same components and means in the control device, previously described as the first aspect of the present invention, other than the first engine restart control means which executes the first engine restart control in which the fuel injection is restarted in order to restart the internal combustion engine without performing the cranking by the starter.

In accordance with a third aspect of the present invention, there is provided a control device for controlling automatic engine stop and start having a starter, a first engine restart control means, and an engine restart ready control means. The starter is comprised of a starter motor for rotating a pinion gear and an actuator capable of meshing the pinion gear with a ring gear. The ring gear is fixed to a crank shaft of an internal combustion engine. The starter independently drives the starter motor and the actuator, respectively. The control device is capable of stopping the internal combustion engine when an automatic engine stop request occurs, and restarting the internal combustion engine when an engine restart request occurs. The first engine restart control means executes a first engine restart control of restarting a fuel injection in order to restart the internal combustion engine without performing a cranking by the starter when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when a current rotation speed of the internal combustion engine is within a first rotation speed range which is higher than a first rotation speed. The engine restart ready control means executes an engine restart ready control for not driving the starter to perform the cranking when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the current rotation speed of the internal combustion engine is within a rotation speed ready range. The rotation speed ready range is not more than the first rotation speed and higher than a second rotation speed. After this control operation, the engine restart ready control means drives the starter motor to synchronize the rotation speed of the pinion gear with the rotation speed of the ring gear when the current rotation speed of the internal combustion engine is within a second rotation speed range which is not more than the second rotation speed and higher than the third rotation speed. After this rotation speed synchronizing operation, the engine restart ready control means drives the actuator to mesh the pinion gear with the ring gear, and then drives the starter to perform the cranking by the starter motor in order to restart the internal combustion engine.

According to the present invention, even if the engine restart request occurs in the rotation speed ready range between the first rotation speed range and the second rotation speed range, it is possible for the control device to smoothly restart the internal combustion engine without performing any complicated engine restart control for estimating the current rotation speed with high accuracy even if the engine restart request occurs during the rotation speed ready range at the boundary of the first rotation speed range and the second rotation speed range. In this control process by the engine restart ready control means, even if the engine restart request occurs when the rotation speed of the internal combustion engine is within the rotation speed ready range, the starter restarts the cranking and the internal combustion engine is thereby restarted after the rotation speed of the internal combustion engine is within the second rotation speed range. Because the period of time for the rotation speed of the internal combustion engine to pass through the rotation speed ready range, it is possible to set the delay period of time to an allowable delay period of time, where the delay period of time is a period counted from the time when the engine restart request occurs to the time when the internal combustion engine is restarted.

In accordance with a fourth aspect of the present invention, there is provided a control device for controlling automatic engine stop and start having a starter, a first engine restart control means, and an engine restart ready control means. The starter is comprised of a starter motor for rotating a pinion gear and an actuator capable of meshing the pinion gear with a ring gear which is fixed to a crank shaft of an internal combustion engine, and the starter independently driving the starter motor and the actuator, respectively, and the control device capable of stopping the internal combustion engine when an automatic engine stop request occurs, and restarting the internal combustion engine when an engine restart request occurs. The first engine restart control means executes a first engine restart control of restarting a fuel injection in order to restart the internal combustion engine without performing a cranking by the starter when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when a current rotation speed of the internal combustion engine is within a first rotation speed range which is higher than a first rotation speed. The engine restart ready control means executes an engine restart ready control for not driving the starter to perform the cranking when the engine restart request occurs while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop and when the current rotation speed of the internal combustion engine is within a rotation speed ready range which is not more than the first rotation speed and higher than a third rotation speed. After this control operation, the engine restart ready control means drives the actuator to mesh the pinion gear with the ring gear when the current rotation speed of the internal combustion engine is within a third rotation speed range which is not more than the third rotation speed, and after or during this gear meshing operation, the engine restart ready control means drives the starter to perform the cranking by the starter motor in order to restart the internal combustion engine.

According to the present invention, even if the engine restart request occurs in the rotation speed ready range which is set between the first rotation speed range and the third rotation speed range, it is possible for the control device to smoothly restart the internal combustion engine without performing any complicated engine restart control for estimating the current rotation speed with high accuracy even if the engine restart request occurs during the rotation speed ready range at the boundary of the first rotation speed range and the second rotation speed range. In this control process by the engine restart ready control means, even if the engine restart request occurs when the rotation speed of the internal combustion engine is within the rotation speed ready range, the starter restarts the cranking and the internal combustion engine is thereby restarted after the rotation speed of the internal combustion engine is within the second rotation speed range. Because the time period necessary for the rotation speed of the internal combustion engine to pass through the rotation speed ready range is short, it is possible to set the delay period of time to an allowable delay period of time, where the delay period of time is counted from the time when the engine restart request occurs to the time when the internal combustion engine is restarted.

Brief description of the drawings

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a view showing a schematic configuration of a control device for executing an automatic engine stop and start routine according to a first embodiment of the present invention;

FIG. 2 is a timing chart showing an engine restart control performed by the control device according to the first embodiment shown in FIG. 1;

FIG. 3 is a timing chart showing a second engine restart control by the control device according to the first embodiment shown in FIG. 1;

FIG. 4A and FIG. 4B are views showing a relationship between a level of sound pressure when a pinion gear is meshed with a ring gear and a difference in rotation speed between the pinion gear and the ring gear;

FIG. 5 is a timing chart showing a third engine restart control by the control device according to the first embodiment shown in FIG. 1;

FIG. 6 is a flow chart showing an engine restart control routine executed by the control device according to the first embodiment shown in FIG. 1;

FIG. 7 is a timing chart showing an engine restart control by the control device according to a second embodiment of the present invention;

FIG. 8 is a flow chart showing an engine restart control routine by the control device according to the second embodiment of the present invention;

FIG. 9 is a timing chart showing a problem caused by the engine restart control;

FIG. 10 is a timing chart showing an engine restart control performed by the control device according to a third embodiment of the present invention;

FIG. 11 is a flow chart showing an engine restart control routine executed by the control device according to the third embodiment;

FIG. 12 is a timing chart showing an engine restart control performed by the control device according to a fourth embodiment of the present invention;

FIG. 13 is a flow chart showing an engine restart control routine executed by the control device according to the fourth embodiment;

FIG. 14 is a view showing an estimated track curve when the rotation speed of the internal combustion engine is decreased after automatic engine stop obtained by the control device according to a fifth embodiment of the present invention;

FIG. 15 is a view showing a method of estimating the track curve when the rotation speed of the internal combustion engine is decreased after the automatic engine stop; and

FIG. 16 is a flow chart showing a track curve estimation routine executed by the control device according to the fifth embodiment of the present invention.

Detailed description of the preferred embodiments

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.

First Embodiment

A description will be given of the engine control device according to a first embodiment of the present invention with reference to FIG. 1 to FIG. 6.

FIG. 1 is a view showing a schematic configuration of the control device 10 capable of executing an automatic engine stop and start routine according to the first embodiment of the present invention.

A description will now be given of a schematic configuration of the engine start control system with reference to FIG. 1.

A starter 11 has a mechanism for pushing the pinion gear to the ring gear when the internal combustion engine 21 is started. The ring gear is fixed to the crank shaft of the internal combustion engine 21. The starter 11 is comprised of a starter motor 12, the pinion gear 13, and an electromagnetic actuator 14. The pinion gear 13 is driven by the starter motor 12. The electromagnetic actuator 14 pushes the pinion gear 13 so as to mesh the pinion gear 13 with the ring gear 23 when the starter 11 starts the internal combustion engine 21.

The pinion gear 13 is arranged to move in the axial direction of the starter 11 in parallel to the axial direction of the crank shaft 22 of the internal combustion engine 21. The electromagnetic actuator 14 is equipped with a plunger 15 and a solenoid 16. The driving force of the plunger 15 is transmitted to the pinion gear 13 through the lever 17, etc. when the starter 11 starts the internal combustion engine 21.

A relay 19 is placed between the battery 18 and the electromagnetic actuator 14. When an engine control circuit (ECU) 20 drives the relay 19 to be electrically turned on, the plunger 15 is moved in the direction so as to push the pinion gear 13 to the ring gear 23. The pinion gear is thereby meshed with the ring gear 23 which is fixed to the crank shaft 22 of the internal combustion engine 21.

A mechanical relay 25 and a switching element 24 are placed between the battery 18 and the starter motor 12. When the ECU 20 drives the switching element 24 to be electrically turned on, the mechanical relay 25 is thereby turned on, and the electric power of the battery 18 is supplied to the starter motor 12. The pinion gear 13 is thereby rotated by the starter motor 12.

The ECU 20 is comprised of a microcomputer. The microcomputer has a built-in read only memory (ROM) in which various types of engine control programs are stored. The ECU 20 executes these engine control programs in order to adjust a quantity of fuel injection and an ignition period of time when the fuel is injected into cylinders of the internal combustion engine 21.

The ECU 20 executes an automatic engine stop and start control routine (not shown) in order to execute the automatic engine stop and start control (that is, the engine idle stop control).

This automatic engine stop and start control automatically stops the combustion of the internal combustion engine 21 in order to automatically stop the operation of the internal combustion engine 21 when the driver stops the vehicle or a speed reduction request occurs during the vehicle running on a road by the following driver's operations, for example:

(c1) The driver of a vehicle releases the acceleration pedal; or

(c2) The driver depresses the brake pedal.

After this, the ECU 20 judges the generation of the engine restart request when the speed reduction request is released during the running of the vehicle or the driver of the vehicle performs the following operations (d1), (d2):

(d1) The driver of the vehicle releases the brake pedal;

(d2) The driver of the vehicle operates the shift lever; or

(d3) The driver of the vehicle depresses the acceleration pedal.

When detecting the above operations (c1), (c2), (d1), (d2), or (d3), the ECU 20 in the control device executes the engine restart control routine by the following procedures.

FIG. 2 is a timing chart showing the engine restart control performed by the control device according to the first embodiment shown in FIG. 1.

As shown in FIG. 2, when the automatic engine stop request occurs, the combustion is stopped in order to automatically stop the operation of the internal combustion engine 21.

During the drop period of the rotation speed Ne of the internal combustion engine 21 by the automatic engine stop control, when the engine restart request occurs in a first rotation speed range (Ne>N1) in which the rotation speed Ne of the internal combustion engine 21 is higher than the first rotation speed N1 (e.g. 500 rpm), the ECU 20 judges that it is possible to restart the internal combustion engine 21 without performing the cranking operation by the starter 11, and the ECU 20 executes the first engine restart control. That is, in the first engine restart control, the control device drives the injectors to inject combustion fuel into the cylinders of the internal combustion engine 21 and ignite the combustion fuel in order to restart the internal combustion engine 21.

This control makes it possible to smoothly restart the combustion of the internal combustion engine 21 immediately when the engine restart request occurs. Because this control does not require any cranking of the pinion gear 13 and the ring gear 23 by the starter 11, it is possible for the starter 11 to have zero power consumption, and to avoid the engagement between the pinion gear 13 and the ring gear 23 when there is a large difference in rotation speed between the pinion gear 13 and the ring gear 23. This control thereby prevents gear meshing noises from being generated.

While the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, when the engine restart request occurs in a second rotation speed range (N1.gtoreq.Ne>N2) in which the rotation speed Ne of the internal combustion engine 21 is lower than the first rotation speed N1 and higher than the second rotation speed N2 (e.g., 350 rpm), the ECU 20 executes a second engine restart control because judging the difficulty to smoothly mesh the pinion gear 13 with the ring gear 23 unless the rotation speed of the pinion gear 13 is synchronized with the rotation speed of the ring gear 23. In the second engine restart control, the ECU 20 in the control device executes the following control: (e1) The rotation speed of the pinion gear 13 is increased by the starter motor 12 in order to synchronize the rotation speed of the pinion gear 13 with the rotation speed of the ring gear 23; and (e2) After the step (e1), the ECU 20 drives the electromagnetic actuator 14 to start the cranking in order to mesh the pinion gear 13 with the ring gear 23. After this gear meshing control, the internal combustion engine 21 is restarted.

FIG. 3 is a timing chart showing the second engine restart control executed by the control device according to the first embodiment shown in FIG. 1.

In particular, as shown in FIG. 3, the ECU 20 drives the starter motor 12 to be electrically turned on in order to rotate the pinion gear 13 at the time t1 when the engine restart request occurs in the second rotation speed range of the rotation speed Ne of the internal combustion engine 21. The ECU 20 judges that the rotation speed of the pinion gear 13 is synchronized with the rotation speed of the ring gear 23 at the time t2 when the difference in rotation speed between the ring gear 23 and the pinion gear 13 is within a range of .+-.200 rpm. The ECU 20 drives the electromagnetic actuator 14 to be electrically turned on and drives the starter 11 to start the cranking in which the pinion gear 13 is completely meshed with the ring gear 23 in order to restart the internal combustion engine 21. The difference in rotation speed between the ring gear 23 and the pinion gear 13 is equal in meaning to the difference of the rotation speed which is a reduced value of the crank shaft 22.

The above control makes it possible to decrease the delay counted from the time when the engine restart request occurs to the time when the internal combustion engine 21 is restarted while smoothly meshing the pinion gear 13 with the ring gear 23 and suppressing gear meshing noises from being generated.

Further, the above engine start control does not need to detect the rotation speed of the pinion gear 13 and the ring gear 23 with high accuracy when the ECU 20 judges the synchronization in rotation speed between the pinion gear 13 and the ring gear 23. It is thereby possible for the control device to be equipped with a usual rotation speed sensor without an expensive crank angle sensor and rotation speed sensor with high accuracy. This feature can reduce the manufacturing cost which is a recent important technical issue.

In the first embodiment described above in detail, the ring gear is 300 mm in diameter (outer diameter of tooth tip) and the pinion gear 13 is 30 mm in diameter (outer diameter of tooth tip). For example, when the ring gear rotates at the rotation speed of 300 rpm, and the pinion gear rotates at the rotation speed of 1000 rpm, the difference in rotation speed between the ring gear 23 and the pinion gear 13 is 200 rpm, where the difference in rotation speed is the different value which is a reduced value of the rotation speed of the crank shaft 22. Because the ring gear 23 is 300 mm in diameter and rotates at 300 rpm, the circumferential speed at the pitch circle (as a virtual circle which is contacted with the tooth of the pinion gear 13) of the ring gear 23 is approximately 4.7 m/sec.

Further, because the pinion gear 13 is 30 mm in diameter, and rotates at 1000 rpm, the circumferential speed at the pitch circle (as a virtual circle which is contacted with the tooth of the ring gear 23) of the pinion gear 13 is approximately 1.6 m/sec. The difference in circumferential speed between the pitch circle of the ring gear 23 and the pitch circle of the pinion gear 13 is approximately 3.1 m/sec. The following condition (f1) is therefore equal to the following condition (f2): (f1) The difference in rotation speed between the ring gear 23 and the pinion gear 13 is within a range of .+-.200 rpm; and (f2) The difference in circumferential speed between the pitch circle of the ring gear 13 and the pitch circle of the pinion gear 13 is within a range of .+-.3.1 m/sec.

The inventors of the present invention did the experiment of detecting gear meshing noises when the pinion gear 13 is meshed with the ring gear 23. FIG. 4A and FIG. 4B are views showing the experimental results which show a relationship between a level in sound pressure when the pinion gear 13 is meshed with the ring gear 23 and a difference in rotation speed between the ring gear 23 and the pinion gear 13.

The experiment detected gear meshing noises generated between the ring gear 13 of 300 mm diameter and the pinion gear 13 of 30 mm diameter by changing the difference in rotation speed between the ring gear 23 and the pinion gear 13 which are meshed together. The gear meshing noises were detected by a microphone which was separated in distance from the pinion gear 13 and the ring gear 23.

The experimental results shown in FIG. 4A and FIG. 4B clearly show that it is possible to adequately reduce the mesh noise when the pinion gear 13 is meshed with the ring gear 23 under the following conditions: (g1) The difference in rotation speed between the ring gear 23 and the pinion gear 13 is within a range of .+-.250 rpm; and (g2) More preferably, the difference in rotation speed between the ring gear 23 and the pinion gear 13 is within a range of .+-.200 rpm (that is, the difference in circumferential speed between the pitch circle of the pinion gear 13 and the pitch circle of the ring gear 23 is within a range of .+-.3.1 m/sec).

The description continues in the full USPTO document.